After a well has been drilled and casing has been cemented in the well, one or more sections of the casing adjacent to formation zones may be perforated to allow fluids from the formation zones to flow into the well for production to the surface or to allow injection fluids to be applied into the formation zones. A perforating gun string may be lowered into the well to a desired depth, and the guns fired to create openings in the casing and to extend perforations into the surrounding formation.
Shaped charges are commonly used in perforating guns to create openings in the casing and channels in the formation zones. To yield best results for deep penetration, shaped charge liners may be made of pure metals due to their great density and ductility. However, liners made of pure metals may form slug that remains in the penetration channels. As a result, the penetrated hole can be plugged, which may interfere with the influx of production fluids, e.g., oil. To overcome this problem, liners used for downhole operations may be made of metal powders, such as pseudo-alloys. If unsintered, the liners may yield jets that are mainly composed of dispersed fine metal particles. To enhance penetration, powdered metal liners may contain high density metal powders, such as tungsten powders (mass density=19.3 g/cm3), as major components.
U.S. Pat. No. 7,811,354, issued to Leidel et al., discloses the use, of a liner for a shaped charge having a high performance powdered metal mixture to achieve improved penetration depths during the perforation of a wellbore. This mixture includes powdered tungsten (92-99%), powdered metal binder (1-8%), and a lubricant, such as graphite, which can be compressively formed into a substantially conically shaped liner.
U.S. Pat. No. 6,564,718, issued to Reese et al., discloses a liner for a shaped charge formed from a mixture of powdered heavy metal and a powdered metal binder. The liner is formed by compression of the mixture into a liner body shape. The mixture contains a range of 90 to 97 percent by weight of powdered heavy metal, and 3 to 10 percent by weight of the powdered metal binder. Specifically, the preferred powdered heavy metal is tungsten, and the preferred powdered metal binder is copper. A lubricant, such as graphite powder or oil, can be intermixed with the powdered metal binder to aid in the formation of the shaped charge liner.
Although these approaches improve the performance of shaped charges, further improvements to methods for fabricating shaped charges that can achieve better penetration in downhole operations would be useful.